This invention relates to a method and algorithm for controlling the amount of xe2x80x9cditheringxe2x80x9d or preloading of a cyclic valve system.
Valve systems are known which are cyclically opened and closed. In many of these systems the speed of the opening and closing cycle may vary as the device associated with the valve system also changes in speed. One challenge is to associate the control sending the signal to open and close the valve in a proper timed fashion with the actual operation of the valve. Most valves have some xe2x80x9clagxe2x80x9d time associated with their operation.
One recent application of such valves is to camless engine technology. A camless engine employs solenoid actuators to control hydraulic fluid flow and operate the valves of the engine rather than an engine cam. In the typical engine, a cam mechanically rocks open and close the valves of a combustion chamber of an engine. Thus, timing is a simple method of cam position. For a camless engine, however, the valves are actuated by electromagnetic plungers tied to an engine control unit. Camless engines may be more fuel efficient than engines using cams, however, timing is not as easily achieved.
Correct engine timing is as important to a camless engine as it is to a cam engine. However, there are challenges to the design of a camless engine not present for conventional engines. Specifically, the solenoids and hydraulic valves introduce a certain amount of lag. This lag may arise from the additional time required to charge the solenoid valves as well as to actuate the hydraulic valves of the system. At lower speeds this lag is particularly pronounced and presents challenges.
One proposed way to cure this lag has been to dither the electromagnetic plunger to prime the system for correct engine timing. For example, a series of short electrical signals may be sent to the electromagnetic plunger actuating the plunger and thereby allowing hydraulic fluid flow to begin actuating the hydraulic valve. After the electromagnetic plunger and the hydraulic valve are primed, then the engine control unit sends an xe2x80x9cevent signal,xe2x80x9d either fully opening or closing the valve, for the desired duty cycle of the event.
Such a system would have a significant drawback. As a consequence of sending numerous priming signals prior to sending an event signal, large amounts of energy are consumed by the electrical system. Thus, employing the strategy may not be practical.
A need, therefore, exists for an engine control strategy that consumes less energy than existing techniques.
In general, the present invention utilizes a system which xe2x80x9cdithersxe2x80x9d or preloads a cyclically operating valve system in such a fashion that the amount of dithering changes as the speed of operation of the valve system changes. Generally, as the cycle time for the valve is reduced the amount of necessary preloading to reduce lag time is also reduced. Thus, as the cycle time decreases the amount of dithering decreases.
One preferred application of the present invention offers an inexpensive and economical engine management strategy. Rather than employing the same dithering scheme throughout the entire range of engine speeds, the invention employs a dithering scheme that varies with engine speed. Accordingly, a dithering signal is communicated to an actuator of the camless engine. The signal activates the actuator for a portion of an event time period less than the event time period. An event signal is sent to the actuator that lasts the entire event time period, activating the actuator for this period. The engine speed is sensed. Then, based upon this sensed speed, the dithering signal may be altered. For example, in some cases plural dithering signals may be sent prior to the event signal. In such a system the number of dithering signals could decrease as the speed of the camless engine increases. Additionally, the length of each dithering signal may decrease as the speed of the camless engine increases. This vary the dithering signal based on engine speed thereby results in significantly less consumption of energy during operation of the vehicle engine.
Such a strategy may be employed for the air intake and exhaust valves of a combustion chamber of the engine. In addition, the technique may be employed for a fuel injector system.
Moreover, the signal strategy may only alter the dithering signals over selected ranges of engine speeds. The dithering signals may also vary from each other. Thus, the strategy permits flexibility in the dithering of the camless engine. The technique employs existing hardware as well to avoid expense. The technique may use existing engine control units and a crank position sensor. This hardware is already in use with current camless engines.
The disclosed system utilizes a solenoid which is driven to open and close and allow the flow of hydraulic fluid to the actual valve. It is a solenoid valve which is xe2x80x9cditheredxe2x80x9d to begin the flow of hydraulic fluid and preload the hydraulic valve.
However, it should be understood that the basic concept can be expanded to any type of valve system which may benefit from the xe2x80x9cpreloadingxe2x80x9d as mentioned above. Generally, any valve which has a cyclic operation time which varies across the range of the system associated with the valve system may benefit from this invention.